Dentinal desensitizing compositions

ABSTRACT

A composition containing a water soluble or water swellable polyelectrolyte mixed salt in a dentifrice base or other oral compositions which can be used for relieving pain and discomfort caused by hypersensitive teeth.

BACKGROUND OF THE INVENTION

This is a continuation-in-part of application Ser. No. 07/811,811, filedDec. 20, 1991, and now U.S. Pat. No. 5,270,031.

Hypersensitive teeth can cause pain and discomfort when subjected tochanges in temperature, pressure, or chemical action. Exposure of thedentin frequently leads to hypersensitivity. Dentin exposure may occurdue to recession of the gums, periodontal disease and improper dentalcare. The usual method of treating hypersensitive teeth employs adesensitizing dentifrice or solution. Some of the active ingredientsused in desensitizing dentifrices include strontium chloride, strontiumacetate, potassium nitrate, and potassium chloride. Other treatments areapplied professionally as a solution. These include solutions of ferricoxalate or potassium oxalate.

One approach to desensitization is to occlude exposed dentinal tubules.Dentinal tubules lead from the pulp to the surface of the dentin. Whenthe surface of the tooth is eroded, the dentinal tubules become exposedto the external environment. The exposed dentinal tubules provide apathway for transmission of fluid flow to the pulpal nerves and this isinduced by changes in temperature, pressure and ionic gradients. Byblocking the tubules, the external stimuli have a diminished effect, andless pain will be felt.

Some active ingredients, such as ferric oxalate, are known to formmineral deposits on the surfaces of exposed dentinal tubules,effectively blocking the openings. In some cases, the abrasive actionfrom brushing may cause a smear layer to form over the surface of thetooth and thus plug up the open tubules. The accumulation of particulatematter from the interstitial fluid passing through the dentinal tubulesor remineralization within the tubules can cause a natural occlusion ofthe tubules.

Nerve inactivation is another mechanism whereby desensitization canoccur. This relies on the action of an active ingredient such aspotassium nitrate on the nerves. By altering the ionic balance in thenerve, the threshold of nerve stimulation is increased. Thus a higherlevel of stimulation is needed to evoke a painful response.

The materials which have been used as active ingredients in thetreatment of hypersensitive teeth are generally inorganic salts orhydrophobic compounds. Although hydrophilic polymers have been used inoral compositions as excipients or the like, they have not beensuggested as being useful active ingredients for desensitizationpurposes. Most of the hydrophilic polymers have been used to control theviscosity of the oral formulation or to give it thixotropic properties.

An example of such a polymer is polyacrylic acid which is used as athickener in dentifrice formulations. It has also been used in gels,mouthwashes and buccal adhesive patches. However, polyacrylic acid hasalso been used for other purposes. For example, Leonard et al. (U.S.Pat. No. 5,011,830) state an oral composition containing an alkalipyrophosphate salt, a fluoride salt and a polyacrylic acid or acopolymer of acrylic acid and another monomer can provide enhancedanti-calculus benefits. Gaffar (U.S. Pat. No. 3,956,480) uses an anionicpolymer such as polyacrylic acid with chlorhexidine as an anti-calculusagent. Benedict and Sunberg (U.S. Pat. No. 4,661,341) describe the useof polyacrylic acid or copolymers of polyacrylic acid as anti-calculusagents. In none of the examples above or elsewhere, as far as we areaware, are these polymers claimed to provide a desensitizing effect.

It has now been determined that certain water soluble or water swellablepolyelectrolytes, i.e. polymers with functional groups that are capableof bearing one or more charged groups in an aqueous solution havedesensitizing properties.

It is accordingly the object of this invention to provide new dentinaldesensitizing agents. This and other objects of the invention willbecome apparent to those skilled in this art from the following detaileddescription.

SUMMARY OF THE INVENTION

This invention relates to an oral composition and method which is usefulfor relieving pain and discomfort caused by hypersensitive teeth. Moreparticularly, the invention relates to the use of certain water solubleor water swellable polyelectrolyte partial salts as a dentaldesensitization agent. The cations used to make the salt can includeammonium, alkylammonium, calcium, sodium, potassium, strontium,magnesium, zinc, aluminum, tin, iron, barium, lanthanum, titanium,bismuth and copper. The salts may contain single cations or mixedcations.

The polymer and its salts may be formulated into a dentifrice, gel,buccal adhesive patch, mouthwash, lozenge, or gum. Use of these oralcompositions on a regular basis can provide relief from the pain anddiscomfort of hypersensitive teeth. The oral composition described abovemay also provide for a sustained release mode of action for the deliveryof strontium or potassium ions from the water soluble or water swellablepolyelectrolytes. The polyelectrolytes may also be used in conjunctionwith additional desensitizing agents such as strontium chloride orpotassium nitrate in an oral composition. In addition a source offluoride ion can be incorporated into the composition.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, a water soluble or waterswellable polyelectrolyte partial salt is used as a dentinaldesensitizing agent. The agent can be incorporated into a dentrifice,gel, mouthwash, lozenge, buccal adhesive patch, gum or the like. Thewater soluble or swellable polymer is an acrylic acid polymer (whichterm includes acrylic acid copolymers). Polyacrylic acid can beobtained, for instance, from B. F. Goodrich under the tradenameCarbopol® or Noveon® as a cross-linked polyacrylic acid genericallycatagorized as carbomer or polycarbophil. Polyacrylic acid can also beobtained from Rohm and Haas under the tradename Acusol™.

The commercially available polymers are produced over a range ofmolecular weights. Thus, for instance, Carbopol® and Noveon® areavailable in different grades with different rheological properties. Thedifferent grades range in molecular weight from 450,000 (907 type) to4,000,000 (980 type). It is preferable to employ the highest molecularweight grade consistent with the viscosity of the formulation beingprepared and concentration of the agent. The formulations will contain adesensitizing amount which is generally from about 0.1% to 30% by weightof the polymer partial salt, with about 1-15% being preferred and about2-12% most preferred. For any given concentration, viscosity generallyincreases with molecular weight and for any given molecular weight,viscosity generally increases with concentration.

The properties of the polyacrylic acid are modified to obtain the mostadvantageous properties by partial neutralization. The cations may bepresent in the salts at about 20% to 100% equivalent mole ratio of thepolymer. The preferred range is from about 40% to 90% equivalent of thepolymer. The cations that can be used include ammonium, alkylammonium,calcium, sodium, potassium, strontium, zinc, aluminum, magnesium, tin,iron, barium, lanthanum, titanium, bismuth and copper. The cations canbe used singly or as a mixture of different cations. These salts as suchare well known in the art.

The salts of the polymer can be made by making a solution of the polymerin water and then adding ammonia or a metal salt such as the hydroxide,carbonate, bicarbonate, oxide, acetate, citrate, lactate, formate orphosphate. The metal salt is preferably alkaline. The solution isstirred, with heating if necessary, until the polymer has dissolved. Itwill usually have a pH between about 3.5 and 9, depending on the amountof metal salt used. The salt solution can be directly incorporated intoan aqueous oral composition. Alternatively, the solution can beevaporated to dryness to give a solid salt which can be milled to a finepowder, if desired, and incorporated into an oral composition.

In order to modify the physical properties of the oral composition, itis preferred to utilize an alkali metal or ammonium salt of thepolyelectrolyte partially substituted with 0,005 to 0.4, preferably0,015 to 0.25, mole equivalent of calcium, zinc or other multivalent(divalent or polyvalent) cation. These cations may include but are notlimited to zinc, tin, magnesium, strontium, copper, iron, bismuth,aluminum and bis(biguanidinium). Adding the cation in such a way as tofavor intramolecular crosslinking can have the advantage of reducing theviscosity and hence improving the organoleptic characteristics of theoral composition without hindering the ability of the composition toreduce dentin fluid flow.

Oral compositions describing polyacrylate polymers partially substitutedwith multivalent metal salts have been described. Gaffar in U.S. Pat.No. 4,138,477 discloses the use of zinc polymer combinations formed bythe reaction or interaction of zinc compound with an anionic polymer asoral compositions to control mouth odor. The purpose of that inventionis to have the complex adhere to the tissues of the oral cavity whereslow release of zinc occurs.

U.S. Pat. No. 4,296,096 to Pierce describes the preparation of a highviscosity dentifrice containing a polyelectrolyte polymer ionicallycrosslinked with aluminum or other polyvalent cation to form particlesless than 74 microns in size. These particles act as a water absorbinginsoluble gel and serve as a dentifrice humectant. Zinc is mentioned asone of the ionic crosslinking agents. The methods of ion-polymer mixingdescribed would result in extensive intermolecular crosslinking of thepolymer. In the present invention, zinc is added under conditions whichwould favor intramolecular crosslinking for the purpose of deswelling ofthe polyacrylic acid gel.

In order to obtain the desired physical properties the following generalprocedure has to be used to fabricate the partially substitutedpolyacrylic acid salt.

First a resin power is dispersed into an acidified aqueous solutioncontaining the desired quantities of the divalent or polyvalent metalsalt. Other desensitizing salts such as KNO₃ can be present in theacidified solution as well. After hydration of the resin is complete, aslurry of an abrasive may be added under high shear. The pH of thedispersion may be adjusted to the desired value by the rapid addition ofan alkaline neutralizing agent under high shear. In order to obtain thedesired physical properties it is important to raise the pH of thedispersion rapidly, e.g., at least four pH units per minute. Finally thefoaming agent, fluoride, flavors and other desired ingredients areblended in.

The polymer salt can be formulated into a dentifrice, mouthwash,lozenge, buccal adhesive patch or gum using ingredients and procedureswhich are well known and commonly used in preparing these oralcompositions. By way of example, without limitation, it is possible toincorporate a fluoride source into the oral composition. Of course, theingredients used to make the above oral compositions should becompatible with the polymer and its salts. It is also possible toformulate the oral compositions in conjunction with additionaldesensitizing agents. Additional desensitizing agents include, withoutlimitation, sodium fluoride, sodium silicofluoride, zinc chloride,formaldehyde, glycerin and silver nitrate. Additional desensitizingagents may also include potassium-containing compounds, such aspotassium nitrate, as described in U.S. Pat. No. 3,863,006 andstrontium-containing compounds, such as strontium chloride, as describedin U.S. Pat. No. 3,122,483.

The polyacrylic acid partial salts have an affinity for the toothsurface and can maintain their presence over a period of time. Thisallows for a longer term availability of the actives fordesensitization.

In order to further illustrate the present invention, variousnon-limiting examples are set forth below. In these examples, asthroughout this specification and claims, all temperatures are indegrees centigrade and all parts and percentages are by weight unlessotherwise indicated.

EXAMPLE 1

A gel containing a sodium (80% equivalent) salt of polyacrylic acid wasprepared from the following ingredients:

    ______________________________________    INGREDIENT      % WEIGHT    ______________________________________    Polyacrylic Acid                    2.9%    Sodium hydroxide                    1.3%    Glycerin        21.0%    Potassium Nitrate                    5.0%    Water           69.6%    Sodium Fluoride 0.2%    ______________________________________

EXAMPLE 2

A dentrifice containing 5% polyacrylic acid (85% equivalent sodium salt)was prepared from the following ingredients:

    ______________________________________    INGREDIENT        % WEIGHT    ______________________________________    Carbomer          4.0%    Sodium hydroxide  1.8%    Glycerin          20.0%    Potassium Nitrate 5.0%    Silica            3.9%    Poloxamer 237     2.5%    Flavors & Preservatives                      0.7%    Water             61.9%    Sodium Fluoride   0.2%    ______________________________________

EXAMPLE 3

A mouthwash was made by mixing the following ingredients:

    ______________________________________    INGREDIENT          % WEIGHT    ______________________________________    Polyacrylic acid (Na/Zn salt)                        2.0%    Alcohol 190 Proof   4.0%    (Grain Alcohol)    Sorbitol            10.0%    Poloxamer 407       2.0%    Flavor              0.3%    Water               81.7%    ______________________________________

EXAMPLE 4

A desensitizing gel dentifrice with fluoride was prepared from thefollowing ingredients:

    ______________________________________    Carbomer           4.2%    Zinc sulfate       0.7%    Hydrochloric acid, 37%                       0.2%    Potassium nitrate  5.0%    Sodium hydroxide   2.2%    Sodium fluoride    0.2%    Glycerin           20.0%    Hydrated silica    5.0%    Poloxamer 237      2.5%    Flavors & preservatives                       1.5%    Water              58.5%    ______________________________________

EXAMPLE 5

A desensitizing gel dentifrice with fluoride was prepared from thefollowing ingredients:

    ______________________________________    Polyacrylic acid     4.0%    Zinc sulfate         0.5%    Hydrochloric acid, 37%                         0.1%    Sodium hydroxide     2.0%    Sodium fluoride      0.2%    Glycerin             20.0%    Hydrated silica      4.0%    Cocamidopropyl betaine, 30%                         6.0%    Flavors & preservatives                         1.5%    Water                61.7%    ______________________________________

EXAMPLE 6

A desensitizing paste dentrifrice was prepared from the followingingredients:

    ______________________________________    Polyacrylic acid     4.2%    Zinc sulfate         0.7%    Hydrochloric acid, 37%                         0.2%    Potassium nitrate    5.0%    Sodium hydroxide     2.2%    Sodium fluoride      0.2%    Glycerin             16.5%    Calcium pyrophosphate                         10.0%    Cocamidopropyl betaine, 30%                         7.0%    Flavors & preservatives                         1.5%    Water                52.5%    ______________________________________

EXAMPLE 7

A desensitizing paste dentifrice was prepared from the followingingredients:

    ______________________________________    Polycarbophil        4.2%    Calcium chloride     0.5%    Hydrochloric acid, 37%                         0.2%    Potassium chloride   3.7%    Sodium hydroxide     2.2%    Glycerin             17.0%    Calcium pyrophosphate                         10.0%    Cocamidopropyl betaine, 30%                         7.0%    Flavors & preservatives                         1.5%    Water                53.7%    ______________________________________

EXAMPLE 8

A desensitizing chewing gum was prepared from the following ingredients:

    ______________________________________    Polyacrylic acid 1.5%    (sodium, zinc) salt    Potassium chloride                     1.6%    Sodium fluoride  0.01%    Gum base         40.0%    Lecithin         0.5%    Flavor           1.0%    Mannitol         3.0%    Sorbitol         52.39%    ______________________________________

EXAMPLE 9

A desensitizing oral lozenge was prepared from the followingingredients:

    ______________________________________    Polyacrylic acid sodium salt                         1.5%    Zinc chloride        0.1%    Sodium fluoride      0.01%    Flavor               0.5%    Sorbitol             97.89%    ______________________________________

Tests Of Oral Compositions Of Examples

The prepared solutions and oral compositions were tested using themethod described by Pashley (J. Periodontology, Vol. 55, No. 9, p. 522,September 1984). This test measures the flow of fluid through a sliceddentin disc. A treatment that will reduce the flow through the discs canalso result in reduced dentinal hypersensitivity for people using thetreatment.

A caries free tooth is sliced to obtain a 0.4 to 0.6 mm thick dentindisc. The disc is mounted in a split chamber device (J. Dent. Research57:187, 1978). The initial flow of fluid through the disc is measured,and then the disc is treated by brushing with one of the desensitizingtreatments. After brushing, the flow rate is again measured and thereduction in flow is calculated from these measurements. The followingcompositions were used and the reduction in flow is reported. Theresults for the dentifrices are based on 1 to 1 dilution with artificialor human saliva.

    ______________________________________    Treatment    % Change in Flow    ______________________________________    Example 1    -48%    Example 2    -63%    Example 4    -97%    Example 7    -80%    ______________________________________

Various changes and modifications can be made in the process andproducts of this invention without departing from the scope thereof. Thevarious embodiments described herein were for the purpose of furtherillustrating the invention but were not intended to limit it.

What is claimed is:
 1. In a gel or paste dentrifice containing adesensitizing amount of a desensitizing agent, the improvement whichconsists essentially of the desensitizing agent being at least one watersoluble or water swellable alkali metal or ammonium salt of an acrylicacid polymer containing about 0,005-0.4 mole equivalent of zinc and inwhich the dentrifice does not contain an additional desensitizing agent,said desensitizing amount being sufficient to reduce dentinal fluidflow.
 2. The dentrifice of claim 1 in which the amount of the member ofthe group is about 0.015 to 0.25 mole equivalent.
 3. The dentrifice ofclaim 1 in which the alkali metal cation is sodium.
 4. The dentrifice ofclaim 1 in which the amount of desensitizing agent is about 0.1 to 30%by weight of the composition.
 5. The dentrifice of claim 4 in which theamount is about 1 to 15% by weight.
 6. The dentrifice of claim 5 inwhich the amount is about 2 to 12% by weight.
 7. In a method ofdesensitizing teeth by applying thereto a desensitizing amount of adentrifice containing a desensitizing agent, the improvement whichcomprises employing the dentrifice of claim 1 as the dentrifice.
 8. In amethod of desensitizing teeth by applying thereto a desensitizing amountof a dentrifice containing a desensitizing agent, the improvement whichcomprises employing the dentrifice of claim 2 as the dentrifice.
 9. In amethod of desensitizing teeth by applying thereto a desensitizing amountof a dentrifice containing a desensitizing agent, the improvement whichcomprises employing the dentrifice of claim 3 as the dentrifice.
 10. Ina method of desensitizing teeth by applying thereto a desensitizingamount of a dentrifice containing a desensitizing agent, the improvementwhich comprises employing the dentrifice of claim 4 as the dentrifice.11. In a method of desensitizing teeth by applying thereto adesensitizing amount of a dentrifice containing a desensitizing agent,the improvement which comprises employing the dentrifice of claim 5 asthe dentrifice.
 12. In a method of desensitizing teeth by applyingthereto a desensitizing amount of a dentrifice containing adesensitizing agent, the improvement which comprises employing thedentrifice of claim 6 as the dentrifice.
 13. The dentrifice of claim 2in which the polymer is a cross-linked homopolymer having a molecularweight of 450,000 to 4,000,000 which is about 40-90% mole equivalentlyneutralized.
 14. In a method of desensitizing teeth by applying theretoa desensitizing amount of a dentrifice containing a desensitizing agent,the improvement which comprises employing the dentrifice of claim 13 asthe dentrifice.